I wonder how firmly your friend believes that nothing is concrete and that A can be both A and Non-A at the same time. To test his committment, you should suggest a little experiment. Get a baseball bat and tell him you're going to swing it at his head. If the bat turns into a wet noodle between the time you start your swing and the time it splits his head open, he wins the argument. If not, he loses both the argument and consciousness. A is A. Believe it.
This was explained well in the Prudent Predator thread. I'll echo what others have already suggested and tell you again that you should go back and read it.
As far as a real world example is concerned, the looming debt crises in Greece, Italy, Spain, Portugal, the US and other countries are the direct result of grandma's system of morality. Social welfare systems like those in the US and Western Europe are fundamentally altruistic in nature. When one pressure group is able to extract wealth from another group at the point of a gun, that system can only function for so long. Eventually the producers tire of being fleeced, they shrug and the system collapses. Of course this may take years to come to a head and grandma might be able to cheat reality for a while and live off of the unearned wealth of others, but eventually that will end. Unfortunately, the end will probably be very bad for everyone and the damage caused by grandma and her system of morality will cause a lot of people to be hurt. I suppose that grandma might even be lucky enough to live like a parasite and die before the day of reckoning comes, but she will have left one hell of a mess for her grandson to sort out.